1. Filed of the Invention
The present invention relates to an electrophotographic photosensitive member, more particularly to an electrophotographic photosensitive member having a protective layer which contains a specific resin and electroconductive particles. The present invention relates to an electrophotographic apparatus and a device unit which employ the photosensitive member.
2. Description of the Prior Art
An electrophotographic photosensitive member must have desired sensitivity, electrical characteristics and optical characteristics corresponding to the applied electrophotographic process. In particular, a photosensitive member of a type that is used repeatedly must have durability against electrical or mechanical external forces repeatedly applied during corona charging, toner development, transference to paper and cleaning.
Specifically, the surface of the photosensitive member must resist wear or damage generated due to friction and deterioration by ozone, which is readily generated at the time of corona discharge when allowed to take place in a high humidity atmosphere. Further, electrophotographic photosensitive members must overcome a problem of adhesion of toner to the surface of the photosensitive member occurring due to repetition of the development operation and during the cleaning operation. Therefore, it has been desired to provide a surface of a photosensitive member which is cleaned rather easily.
In order to meet the various needs for the surface of the photosensitive member, attempts have been made to provide a surface protective layer mainly composed of resin formed on the photosensitive layer. For example, Japanese Patent Application Laid-Open No. 57-30843 has proposed a protective layer capable of having a controlled resistivity by using a mixture of a resin and metal oxide particles as electroconductive particles.
However, the foregoing methods have suffered from unsatisfactory dispersion of metal oxide particles in a binder resin. That problem leads to a defect that the conductivity and the transparency of the protective layer have been adversely affected. Therefore, problems sometimes take place in that the formed image has a defect due to the uneven protective layer, the residual potential undesirably rises after the photosensitive member has been used repeated, and the sensitivity deteriorates excessively. In order to cause the protective layer to have excellent transparency and uniform conductivity, it is very important to disperse very fine particles (having an average primary particle size of 0.1 .mu.m or less). Very fine particles of the foregoing type suffer from unsatisfactory stability as compared with ordinary fine particles (having an average primary particle size of 0.5 .mu.m or more), so that secondary aggregation tends to proceed with time, and the size of the dispersed particle tends to be enlarged undesirably. As a result, there arise a problem of deterioration of the transparency and the uniformity of the conductivity.
To meet growing demands for further improving image quality and durability, an electrophotographic photosensitive member having better electrophotographic characteristics as mentioned above must be developed.